text:
Can a private pilot get an RVSM LOA?
Can a private pilot get a Reduced Vertical Separation Minimums Letter of Authorization from the FAA?
I am looking at this checklist on the FAA site and it asks for a business address. Can private pilots get this as well?

The LOA is not granted to the pilot, but the operator.

Are you asking about flying your own personal aircraft?

@TomMcW It is the company aircraft, but flying is not the business

An RVSM LOA is given to an operator not a pilot.
RVSM airspace can be used under part 91, so it is not limited to commercial operations. It can be a private owner or a non-aviation business. FAA Advisory Circular 91-85A says this:

3.4.1 Who is the Correct Person to Apply for and Have Issued the RVSM Authorization?
  The person exercising operational control of the aircraft during the operation requiring an RVSM authorization is the proper person to be the applicant for that authorization. It is important to note it is the RVSM applicant’s responsibility to submit a request for RVSM authorization in the name of the person having operational control of the aircraft, not the responsibility of the FSDO or a specific ASI to make such a determination. The following general information may be useful in assisting the RVSM applicant in determining if the appropriate party has been properly designated as the legal Operator with respect to the RVSM authorization request:

For non-commercial operations conducted under part 91 and part 125
  (A125 LODA holders), the authorization applicant and legal Operator should normally be one of the following persons, in which event the authorization will be issued in the form of an appropriate letter of authorization (LOA):

A registered owner of the aircraft operating the aircraft incidental to its own non-air transportation business or personal activity.
A person assuming operational control of the aircraft through a lease or use agreement for that person’s operation of the aircraft incidental to that person’s own non-air transportation business or personal activity.

*emphasis mine

So if it is a company plane then the company will be the holder of the RVSM authorization, and there must be a responsible party within the company that is knowledgeable about the operation of the aircraft (i.e. responsible to ensure maintenance requirements are met, the pilots are “RVSM-knowledgeable,” that proper procedures are followed, etc. - not necessarily a pilot).
The authorization will be specific to the aircraft (or a group of similar aircraft) and it must meet the equipment requirements laid out in Part 91 apppendix G.
So, what makes the pilot “RVSM-knowledgeable?”
The same advisory circular says:

3.3.1.1 For an applicant operating only under part 91 or part 125 (including
  A125 Letter of Deviation Authority (LODA) holders), demonstrating it has RVSM-Knowledgeable Pilots will consist of providing sufficient evidence each pilot has an adequate knowledge of RVSM requirements, policies, and procedures as required in part 91 appendix G, section 3(c)(2).

The following are acceptable means for the Operator to show the FAA its pilots have adequate knowledge of the RVSM operating practices and procedures: 14 CFR part 142 training center certificates without further evaluation; certificates documenting completion of a course of instruction on RVSM policy and procedures; and/or an Operator’s in-house training program.

Note: The FAA, at its discretion, may evaluate a training course prior to accepting a training certificate.
*emphasis mine

Most likely, in a non-aviation company there won’t be an acceptable in-house training program, so any pilots will need certificates documenting completion of a course of instruction on RVSM policy and procedures. There are several flight schools with approved courses that can provide such certificates.
What it boils down to is the company that owns or leases the plane must get an LOA for their aircraft. The aircraft must meet RVSM requirements and to use RVSM airspace the pilot also must be certified.
If you own your own aircraft then you are, by default, the operator. So you can apply for an LOA as the operator. You would be your own responsible party and anyone who flies the aircraft in RVSM airspace, be that yourself or someone else, must be an “RVSM-knowledgeable” pilot.
If you rented your personal plane out to someone, say to a flight school, then they would become the operator while it is in their possession, so they would need to have their own LOA to operate in RVSM airspace.


text:
What aircraft maintenance logs should I have available for a private checkride?
I’m about to do my Private Pilot Checkride in my own plane. I’ve been trying to find a list of things that will be needed for the Checkride in the logbook, as I had thought it was an updated annual, ELT battery is within time, and all ADs are complied with. My CFI said he thought it needed other things like VOR checks in the last 30 days and transponder checks and more.  Is there a specific part in the FARs or somewhere that lists out exactly what it needed for VFR day/night flight as far as maintenance logs to keep the plane airworthy? I’m not talking ATOMATOFLAMES, but maintenance logs (aircraft, engine, prop) specific?

You should pose that question to the IA that does your annual.  Transponders require a perf check every two years.  30 day VOR checks are an operational check and only required for IFR use.  Since the PP checkride is a VFR flight, the requirements are the same for any other VFR flight so you'd want your paperwork to be in order same as if you were being ramp checked by an FAA inspector out on your travels.

I recommend looking at the following two videos which will cover almost everything you will need: https://www.youtube.com/watch?v=kr483zBbQKw and https://www.youtube.com/watch?v=zVE-gIeZUpk&t=2s

The answer to your question is in the Private Pilot ‒ Airplane Airman Certification Standards

Task   B. Airworthiness Requirements References   14 CFR parts 39, 43,
  91; FAA-H-8083-2, FAA-H-8083-25

You should read and understand CFR §91.203, §91.205, §91.207, §91.209,  §91.213, and §91.215.
The DPE will want to know that the aircraft is legally permitted to operate in the airspace that you will be taking your practical test in.
They will check that the AR(R)OW documents are in the aircraft—Airworthiness Certificate, Current Registration, probably not Radio License since it is not likely your test will take you to another country, Operating Limitations, and current Weight and Balance. Operating Limitations would include placards; any documents required by STCs for installed equipment e.g. GPS or autopilot; and for newer aircraft flight manual (AFM) for that aircraft.
They will check the logbooks to make sure that the aircraft is legal maintenance-wise. Annual Inspection and 100-hour AD items obviously. Some 100 hour items can be signed off by the pilot e.g. Bendix switch check while others need to be signed off by an A&P e.g. muffler shroud inspection. Most A&Ps use a computer system that prints out a list of ADs and when they were complied with. It is a good idea to put a sticky-note on the annual and recurring ADs pages so you don’t waste time looking for them.
ELTs are usually checked at annual time, but they can get out of sync with the annual and they will check that. If you are taking the test in an aircraft with an electrical system, the transponder must be working and checked in the last 24 months. You don’t need a pitot-static check for a private checkride, but if you are going to file and fly IFR flight plan—as you will for your instrument rating you will need one.
If there is any inoperative equipment e.g. LORAN then it must be logged and marked.
ADSB isn’t required yet, but after January 1, 2020 if you fly in the covered areas your aircraft must have it installed. CFR §91.225.
On an instrument check-ride the DPE will want to see that the database is current if you have a GPS and that the VOR check has been done.
They will also check to make sure that your medical is current and that you have all of the endorsements necessary for the aircraft e.g. complex, high performance, tailwheel.

From https://weflyimc.com/articles/f/aircraft-required-maintenance-inspections---acronym-aav1ate
**Airworthiness Directives 91.417(a)(2)(v)**
    Notifies aircraft owners and other interested persons of unsafe conditions and to specify the conditions under which the product may continue to be operated. They could be either one-time or recurring ADs.
**Annual Inspection 91.409**
    Every 12 calendar months. Can only be performed by an IAP (Inspection Authorized) mechanic. It also can substitute a 100-hr inspection.
**VOR 91.171**
    Every 30 days. Only required for IFR flights.
**100-hour Inspection 91.409**
    Only required if the aircraft is for hire.
    An aircraft can exceed its 100hr inspection only by up to 10 hrs while en route to a place where the inspection can be done. A special flight permit is not needed to fly those 10 hours, but the time must be logged in the maintenance record.
        If an inspection was due at 100hrs but the plane flew 105hrs before it was inspected, the next inspection will still be due at 200hrs.
**Altimeter, altitude reporting and static system 91.411**
    Every 24 calendar months
**Transponder 91.413**
    Every 24 calendar months
**ELT 91.207**
    Every 12 calendar months
    The regulation lists a lot of cases in which an ELT is not required, in which case maintenance is not required. Out of all items in that list there are two which might apply for flight training purposes:
        If engaged in training operations conducted entirely within a 50-nautical mile radius of the airport from which such local flight operations began.
        If temporarily removed  for no more than 90 days for inspection, repair, modification, or replacement, and in its place is a placard stating the removal.

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text:
Why does "V1 increase with decreasing density"?
The statement made in the question is mentioned in one of the renowned publications.
My contradictions which I have already ruled out as a potential solution:

As Density decreases Vmcg decreases thus V1 is not limited by Vmcg.

As Density decreases Vmbe decreases as there's insufficient cooling
of the brakes, thus V1 should ideally be limited by Vmbe.

At lower density the aircraft needs to be at a higher groundspeed to
achieve the same CAS, but the ASDA would be limiting factor as it
would require a greater stopping distance, this would again limit V1.

"in one of the renowned publications" -> why don't you say which one?

Do you disagree with the statement ?

Please provide more of the circumstance surrounding the statement "V1 increase with decreasing density". Are we talking of the FLL, Field Length Limit Weight all the time? Let us assume a balanced field for simplicity. The statement can become correct if we take an actual weight less than the FLL then if we start calculating for lower densities, at some point this same actual lower weight will become the FLL weight. As the density is lowered, at each increment, the  Required FL will increase and it is probable that the V1 will increase along with it.

I guess the statement is about V1 from the balanced field length, which is where the accelerate-go distance is equal to the accelerate-stop distance:

(image source: boldmethod > Engine Failure On Takeoff: Do You Stop Or Go?)
How do these curves change when the density decreases? Lower density means less thrust, therefore accelerating will be slower and uses more distance. This affects both curves equally for the acceleration to V1, but afterwards only the accelerate-go distance:

Let us call the force accelerating the aircraft initially $ F = 2 \times T $ (thrust from two engines).
In the accelerate-go case, you would only accelerate with a force of $ F = T $ after the engine failure.
In the accelerate-stop case, you brake with a certain force $ F = F_\text{brake} $.
Now, at lower density, the thrust $ T $ will decrease, but the brake force $ F_\text{brake} $ will be unaffected.
The accelerate-go case is therefore affected during the entire time by the lower value of $ T $.
The accelerate-stop case is only affected during the accelerate part, but afterwards the brake force is still the same.

Therefore, both curves will move up in the diagram, but the accelerate-go distance will move up more. This implies that their intersection (the balanced field length) will occur further to the right, resulting in a higher value for V1.

If both curves move upwards, wouldn't the net V1 decrease ?

But why would you say that accelerate go distance would, increase more that accelerate stop distance? Is there something I'm missing ? Is it a parametric thing?

That edit makes it much more understandable, appreciate your effort and time  ! Good day @Bianfable

'Now, at lower density, the thrust T will decrease, but the brake force Fbrake will be unaffected.' May I ask how this is possible? With reduced density, the maximum brake energy speed reduces. The brakes becomes more inefficient.

@AnasMaaz The force from the brakes will be the same, regardless of density. The max. brake energy is limited by the kinetic energy of the aircraft, which depends on (ground speed)^2, but Vmbe is given in indicated speed, not ground speed. So the value will change with density, but the braking force and total kinetic energy limit will not.

@Bianfable Not correct. Heated up brakes cannot be as efficient as cool brakes. Vmbe is the speed on the ground at which an aircraft can safely stop within the energy capabilities of the brakes. Above this speed, even if you apply the maximum amount of 'braking force' the brakes cannot safely stop the aircraft.

@AnasMaaz I agree, but the ambient temperature should not have a large affect on the brake temperature. The increase in brake temperature is proportional to the amount of energy absorbed by the brakes and therefore proportional to the aircraft kinetic energy.

It does. It does a lot. I have been an airline pilot for many years now and I see this everyday. Brake temperature has a massive effect on the take off performance. The main reason why A320 has brake fans is to reduce turn around time.

@AnasMaaz I know. I'm not suggesting brake temperature makes no difference. I'm talking about the effect of different densities on the brakes. And AFAIK air density has essentially no effect on the force the brakes can deliver, but maybe I'm wrong about that.

We all know that V1 is limited by both the Vmcg (minimum control speed-ground) and the Vmbe (maximum brake energy). It is also affected by Vr (rotation speed). But that is for some other question. Firstly, V1 cannot be lower than Vmcg because if an engine fails below V1, the air flow over the vertical stabilizer and the rudder is not sufficient enough to control the aircraft. On the other hand, V1 cannot be higher than Vmbe because, if you try to stop the aircraft at a higher speed than Vmbe, the brakes can fail and in worst case catch fire.
If the density is lower, the Vmcg reduces because less thrust is produced by the engines. So, in an engine failure the amount of force that needs to be counteracted by the rudder against the live engine reduces. As, you have mentioned thus with reduced densities, Vmcg does not limit the V1.
A reduction in density reduces the value of Vmbe as well. So, if we consider a balanced field, the value of V1 will be higher than Vmbe. As we have discussed before, this is not an ideal situation. To ensure a safe take off hence, the value of V1 is reduced until it becomes less or equal to Vmbe. This will increase the TODR (Take off distance required) and reduce the ASDR (Accelerate stop distance required). Why does this happen? Any time, the V1 is reduced, the ASDA decreases and the TODR increases. The ASDA decreases because the lower the V1, the earlier it is assumed an engine will fail, so the less the aircraft is accelerated. Therefore, the lesser the acceleration, the shorter the aircraft can be stopped. The TODR increases because a reduced V1 just like before results in a reduced acceleration. It simply takes more distance to take off with one engine operative than with two.
To answer your question. At a lower density, the reduction in Vmbe means, you will have to reduce the value of the V1 to that of Vmbe to get the best field performance. The result is an increased TODR and a decreased ASDA. The total field length required increases because it is limited by the TODR.

The dark dotted line is the ideal V1 which occurs at the balanced field (ASDA = TODR). Here, the value of Vmbe is reduced due to a decrease in density. So, if you reduce the V1 to that of Vmbe, the TODR increases and the ASDA decreases. The yellow line is the total field length and it increases to account for the TODR.

If I understand you correctly, you are saying that V1 must be reduced down to Vmbe, if balanced field length V1 is larger at that density. That makes total sense to me. But what about the case where the balanced field length V1 is still below Vmbe despite the lower density?

What do you mean by V1 going below Vmbe exactly? You can reduce it, but that will increase field length as TODR increases. If you are asking what if the balanced V1 is below Vmbe then that is great. That is what we want. With V1 below Vmbe the aircraft can be safely stopped before V1. Moreover, with a balanced field the total field required reduces.

The whole reason why we bring V1 to the same value of Vmbe is solely to ensure that V1 is equal to Vmbe (V1 should always be less than or equal to Vmbe). If Vmbe is higher than V1 you need not change a thing.

Yes, that is exactly what makes perfect sense to me. But the original question by the OP was: why does V1 increase with decreasing density? So, what happens here if you are not limited by Vmbe?

It doesn't have to. V1 is a flexible value. It can be varied between Vmcg and Vmbe. (Vmcg <= V1 <= Vmbe). So, a reduced density reduces both Vmcg and Vmbe. So, for a given airport with a given pressure altitude and density, a reduced density will result in a reduced V1.

100% agree with that. And it has been my understanding that one typically uses the V1 from the balanced field length, as long as it fulfills the Vmcg <= V1 <= Vmbe requirement. My interpretation of OP's quote was that the balanced field length V1 goes up when density goes down, but since the quote is without context, I'm not sure if they even meant that...

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text:
Why does V165 have two different MEAs over the same route section?

Why does V165 have two distinct MEAs which vary by a large factor (apart from the 180$^{\circ}$ rule of altitudes) considering they would be clearing the same obstacles and receiving signals from the same NAV aids?

Please refer IFR  chart containing V165

If you are jetting along in a certain direction, there might be a big mountain ahead of you. but if  you are tooling along in the opposite direction the mountain will be behind you.  This difference is called out to you so you will be safely boring holes in air instead of granite.

If the obstacle is at the midpoint of the route wouldn't the aircraft have to clear it by the same altitude

@DarshanPatil - Welcome to Aviation! I've added a chart snippet to your question and changed the question slightly to refer to it.  If that's not what you intended, please feel free to edit.

That's great I appreciate it , I was unable to upload the picture myself . Thank you @ Steve V

The most likely reason is terrain. Here's what the VFR sectional looks like:

You can see that the terrain rises sharply to over 3000' close to WINLO intersection, which is too high to provide IFR obstacle clearance (1000', or 2000' over mountainous areas) at an MEA of 4000'. An aircraft flying south on V165 would need to be well above the terrain before reaching WINLO, whereas one flying north from WINLO can use a lower altitude.


text:
What are the Area Control Center (ACC) frequencies for Germany?
I'm looking for the frequencies of all Area Control Centers (ACC) in Germany. What are they, or where are they published?

The radio frequencies used by German ACC sectors are listed in AIP Germany ENR 2.1 (page 36 onward). This is the standard place to find ACC frequencies for any country in the world.
There are too many frequencies to list here, but you can find the full document here. Below is a screenshot of page 36. Column 1 contains the sector name and dimension, column 4 contains the frequency(ies) used by that sector.

Okey I found it out.
The map of Germany ACC sectors you can find here:
https://www.eurocontrol.int/sites/default/files/content/documents/nm/cartography/erc09l-23may2019.pdf
If you have your airway and name of sectors, then you are able to find the frequency on this site:
http://www.aviascan.de/downloads/Sector%20Information%20Manual%20Germany.pdf

The last link you mention is a document from a very old ATC game. You can definitely not trust the information found there.


text:
How does a pilot select the correct ILS when the airport has parallel runways?
How do you not mess up ILS on parallel runways? There are many airports with ILS and parallel runways, how do you select which ILS for the runway you want?
For example there are RWY 22L AND 22R and both of them have ILS enabled. How does the pilot know on which ILS he is flying?

The two ILS approaches on parallel runways will have a different ILS Localizer frequency. The pilots will select the correct approach from the charts and then either manually tune in the correct frequency or (for more modern aircraft) select the approach in the flight management computer, which will then automatically tune the correct frequencies. Before actually flying the approach, the pilots will cross-check the morse code identifier either by listening to it or (for more modern aircraft) by reading it off the displays.
Below you can see the ILS charts for the Runway 27L and 27R approaches at London Heathrow (source). I marked the frequencies and the identifiers (as they will be displayed on the screen, the morse code is depicted below).

where will they manually enter the ils frequency In the airplane?

This depends on the aircraft. On a Boeing 737 for example, there are NAV tuning panels below the COM (voice communication panels).

ILS works with radio waves, just like voice communications, or other navigation aids like VOR. This means a specific approach will use a specific frequency for its navigation signal.
When the pilot is told what approach to expect, they will consult the chart for that procedure for the information needed to fly it. The top left corner of an ILS approach chart from the FAA will show the frequency for this approach:

The pilot will tune the navigation radio to this frequency (or the FMC will do it automatically). Where they do this will depend on the aircraft. On the 737, the radios are tuned on the center console, just behind the throttle quadrant. The navigation radio tuner is just below the communication radio tuner.

Modified from source
Parallel approaches (or nearby ones) will be set up so that they do not interfere with each other and an ILS must be checked periodically to make sure that any deviations are within allowances.


text:
How does a mechanic determine if a repair or alteration requires a Supplemental Type Certificate?
How does a mechanic know when they have exceeded what 14 CFR Part 43 allows for a repair or alteration to an aircraft? They have thus entered an area where the repair/alteration is so significant that the Type Design has been changed, requiring a Supplemental Type Certificate (STC). Do aircraft maintenance manuals give the mechanic some limits to what he can do, or is AC 21.101 all they have to go on?

Maintenance manuals do not cover alterations. They cover maintenance and repair.  Repair is the act of returning an aircraft to airworthy status which requires it to be in conformance with its Type Certificate -- so no STC. If your 'repair' is something other than the original design, it is an alteration. Alterations may be minor or major. Major alterations will require an approval, but it may not require an STC. The AC is the guidance. And its guidance includes contacting the certification office (or a DER) if you have questions.

Good clarification about maintenance manuals not covering alterations.

Repairs and alterations are defined at FAR 1.1, FAR 43 App(A)(a)(1-4), FAR 43 App(A)(b)(1-4)

"Major alteration means an alteration not listed in the aircraft, aircraft engine, or propeller specifications - (1) That might
appreciably affect weight, balance, structural strength, performance,
powerplant operation, flight characteristics, or other qualities
affecting airworthiness; or (2) That is not done according to accepted
practices or cannot be done by elementary operations."
Minor alteration means an alteration other than a major alteration.
Major repair means a repair: (1) That, if improperly done, might
appreciably affect weight, balance, structural strength, performance,
powerplant operation, flight characteristics, or other qualities
affecting airworthiness; or (2) That is not done according to accepted
practices or cannot be done by elementary operations.
Minor repair means a repair other than a major repair.

In the US, to be airworthy (FAR 21.183) all aircraft must "conform to type design and condition for safe flight". To "conforms to type design" there must be some type of approved authorization for every piece on the airplane. There are several ways to do this.

The manufacture may have pre-approved the equipment you wish to install. Under CAR 1,2, & 3 (~prior to 1958) regulations a separate document for the aircraft called a "data sheet" showed approved equipment. After 1958 aircraft where certified under FAR's and used a "Equipment List". The "Equipment List" for light aircraft is usually found at the back of the Pilot Operating Handbook (POH). An example for a 1978 C152 is shown below.

If a manufacture did not approve the equipment than it may be installed under the authority of a "STC" (equipment pre-approved by the FAA).

...or an "alteration" that a AI (Authorized Inspector) gets approval from the local FAA FSDO office by filling out Form 337 and have it field approved.

The owner is required to keep a copy of either a "STC" or Form 337 "alteration" to show the equipment is legal for each annual inspection. If an aircraft has equipment installed that is not authorized by a Data Sheet, Equipment List, STC, or Form 337, the aircraft is un-airworthy and illegal to fly.
There are three small exceptions:

The FAA provides an alternate approval for small common parts (FAR 21.303-4 and Court Order 8110-42A)
such as wheel bearings, chemicals i.e de-iceing fluid, etc via a "PMA" authorization.

The FAA approves replacement of some parts that meet industry
standards (AC 20-62e) without need of authorization for parts such as sheet metal,
electrical components, minor hardware, etc.

In certain circumstances (FAR 21.303-2 and AC 20-62e) the owner may have a part built or manufactured that is no-longer available for purchase. This provision is often used for old bi-planes and war birds.

Great answer, thank you for pointing out some of the differences between repair,  alterations and type design.

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text:
Are there downloadable versions of the Canadian VNC and VTA charts?
Are there PDF versions of Canadian VNC and VTA charts available for download? I fly in Australia where airservices lists them on their website so I was hoping to find something similar for Canada.

There is a plan to produce electronic versions but they don't seem to be available yet and you can still only order paper ones.  Go here:
http://www.navcanada.ca/EN/products-and-services/pages/aeronautical-information-products-charts.aspx

Do you have any reference to the planned electronic version introduction of those (official announcement, ...)?

Well this is disappointing.  My information was quite out of date.  It seems Nav Canada has decided to farm out Canadian charts to Foreflight, which requires you to buy their subscription.  https://www.foreflight.com/support/faqs/canada/

Also: http://www.navcanada.ca/EN/media/pages/publications-corporate-direct-route-story-2.aspx


text:
How is maximum rate of climb defined in aircraft specifications?
In common aircraft specifications a "rate of climb", or "maximum rate of climb" is specified. For example the wikipedia page for a Spitfire, or C172.
However my intuition is that the rate of climb depends wildly on various things. Aircraft weight, altitude and so on. Furthermore, you could potentially fly at maximum airspeed, and then pitch up 90 degrees, and climb until you begin to stall. Sure you wouldn't be able to last long, but for a short period you'd have a very high rate of climb.
So the question really is, when aircraft specifications detail "rate of climb", is there some implicit context for when that rate of climb is applicable? Is it optimized for climbing in the most time or distance efficient way for X distance or something?

The "maximum rate of climb" is the highest sustainable ROC for the following conditions...

sea level conditions (or standard atmosphere for other altitudes)
maximum gross or takeoff weight
cruise configuration
maximum rated continuous thrust/power

There are additional minor requirements given in FAR 23 such as the rated power 8 seconds (SFAR to 23, par 6 and 23.63-23.67) after the throttles are moved to the full thrust position but the above is a good generalization.

It looks like the FARs usually define the minimum ROC, not the maximum (e.g. 23.2120, 25.119, 25.121). And as a minor point, 23.63-67 aren't current any more although obviously many aircraft were originally certified under them.

The term is referring to the maximum rate of climb as in the best that the aircraft can achieve, not a regulatory limit on rate of climb.

What does sustainable mean exactly? That you can sustain this rate of climb until you reach your max altitude?

"sustainable" means consistent attitude & speed over a reasonable period of time. Diving and pulling up would not be "sustainable".

@jwzumwalt, You write:  «Further more, you could potentially fly at maximum airspeed, and then pitch up 90 degrees »: the issue here is not the rate of climb but the rate of pitch, doing this will at least damage the structure of a long aircraft, modern aircrafts Boeing +Airbus, are protected for pitch rate and for pitch, as a consequence  for the rate of climb.


text:
Why is there a relationship between maneuvering speed and weight?
Could you explain the relationship between maneuvering speed and weight?
Why are they linked?

https://www.aopa.org/news-and-media/all-news/1999/march/flight-training-magazine/a-new-look-at-maneuvering-speed  Somebody could turn that article into a good answer with a little selective copy/paste work.

stall speed goes up as weight increases. Since maneuvering speed is set a certain margin above stall speed, it goes up too as weight increases.

Maneuvering speed is called corner velocity on the military. It is the lowest airspeed at which you can generate Lift equal to the aircraft weight times the maximum allowable load factor or "G". Obviously, a given specific aircraft configuration determines a specific Lift Coefficient function (specifying the lift coefficient for each angle of attack.) This function has a peak (the maximum value of the lift coefficient) which occurs at what is defined as stall Angle of attack (AOA). This stall AOA is the AOA that will generate the maximum lift available at any airspeed. But as Lift is a function of the lift coefficient times the airspeed squared, the higher the airspeed the more lift is generated at that maximum lift AOA. Below Corner velocity or maneuvering speed, as you increase AOA, the lift (and the Load factor or G-load) increases until you reach maximum Lift OA, then if you increase AOA beyond that point, lift decreases as the wing stalls.
Above Corner velocity or maneuvering speed, however, as you increase AOA, the lift,(and the Load factor or G-load) increases beyond the aircraft Maximum load factor or G-Load before you reach maximum Lift AOA, and you can overstress the aircraft.
The higher the gross weight of the aircraft, the lower the Load factor as a result of any specific amount of lift being generated by the wing (Load factor is of course Lift divided by gross weight). But it is the actual Lift (the forces), that produce stress on the structure of the airframe (wing spars, etc.) not the load factor. The airframe is designed to withstand a specific amount of stress (or lift force). SO, at higher gross weight, the allowable load factor (or aircraft G) will be lower, because the maximum allowable lift (which will cause the maximum allowable stress on the airframe) will generate a lower amount of aircraft G.
In the military we used a diagram called a Vn diagram. This is a graph of airspeed versus Aircraft G-Load at a specific gross weight.

The upper left curve represents flight at maximum Lift Angle of Attack (AOA). the upper horizontal boundary represents the maximum allowable load factor or G-loading. The upper left corner, (labeled Maneuvering speed) is the intersection of upper left curved (maximum AOA) boundary of the flight envelope, and the upper horizontal (Load factor) boundary .
Because gross weight decreased the load factor at which maximum lift would be attained, there was a different chart for each gross weight. The higher the gross weight, the smaller the flight envelope became. The upper (maximum AOA) boundary moved down and to the right (since the same AOA at higher gross weight would produce less Load factor or aircraft G), and the upper horizontal boundary would also move down (for the same reason).

Maneuvering and turbulence create loads on the air frame. In the case of maneuvering, any time you change your direction you are accelerating, in that direction. Newton's second law says any time you have acceleration, you must have a force and the force is that mass of the object multiplied by the acceleration. In aviation, this acceleration is generally talked about in "g-forces," which is the ratio of the rate acceleration vs the acceleration rate of gravity.
Further, if you think as maneuvers as simple turns (or pitch) around a given radius, you can calculate the acceleration by a = v^2/r, where v is velocity (speed) and r is radius. Therefore, high speed drives higher acceleration, which drives higher forces.
Since the force acting on the aircraft is the acceleration multiplied by the mass, the larger than mass the higher the force. This force must be reacted out through the aircraft structure. For example, if an aircraft pulls a positive 3g, the wings must carry 3 times the aircraft weight, engine mounts must carry 3 times the engine weight, the cargo floor has to carry 3 times the cargo weight, etc.
Therefore, it is a design trade off. If the same maneuvering speed is allowed throughout the weight envelope the structure must be stronger, which also makes it heavier. If a lighter air frame is desired, maneuvering speed can be reduced at higher gross weights.

Section 2.14.2 Maneuvering Speed of See How It Flies by John S. Denker explains the relationship between mass (not weight) and maneuvering speed.

Unlike $V_{NO}$, the maneuvering speed varies in proportion to the square root of the mass of the airplane. The reason for this is a bit tricky. The trick is that $V_A$ is not a force limit but rather an acceleration limit. When the manufacturers determine a value for $V_A$, they are not worried about breaking the wing, but are worried about breaking other important parts of the airplane, such as the engine mounts. These items don’t directly care how much force the wing is producing; they just care about the acceleration they are undergoing.
By increasing the mass of the airplane, you decrease the overall acceleration that results from any overall force. (Of course, if you increase the mass of cargo, it increases the stress on the cargo-compartment floor — but it decreases the stress on unrelated components such as engine mounts, because the acceleration is less.)
This means you should put $V_A$ along with $V_S$ and $V_Y$ etc. on your list of critical airspeeds that vary in proportion to the square root of the mass of the airplane. However, $V_A$ depends on real mass not on weight, so unlike the others it does not increase with load factor.

Later in the same section, the author clarifies.

Finally, we should note that there are two different concepts that, loosely speaking, are called maneuvering speeds.

The design maneuvering speed, which we can denote $V_{A(D)}$, is primarily of interest to aircraft designers, not pilots. The designer must choose a value for $V_{A(D)}$ and then build an aircraft strong enough to withstand certain stressful maneuvers at that speed. Higher values of $V_{A(D)}$ promote safety, by forcing the design to be stronger.
The maneuvering speed limitation, which we can denote $V_{A(L)}$, is of interest to pilots. It is an operating limitation. It appears on a placard in the cockpit. Lower values of $V_{A(L)}$ promote safety, by restricting certain operations to lower, less-stressful airspeeds.

wrong. It is the actual force, NOT the acceleration, that engineers are concerned about. Acceleration does not break anything. Stress, from forces, breaks critical; airframe and/or engine components. The higher the gross weight of the aircraft, (and the mass) the lower the acceleration that will be produced by whatever critical amount of lift (force) is sufficient to break something. That is why the acceleration or load factor limits decrease as gross weight increases.

Also, although I cannot be sure, it sounds like the author might believe that the it is the airspeed itself that can effect damage. If so, this is also wrong, Maneuvering speed is simply the minimum airspeed at which it is possible, (by establishing the angle of attack that produces the maximum possible coefficient of Lift - Clmax), to generate sufficient stress on critical airframe components to damage them.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What is the wingtip station number on a Boeing 747?

In the figure we can see the station line even though it is not clear. I'am using that picture just for an example to make the question clearer.
Main question

What is the station number for wingtip on a Boeing 747? (fuselage station and water lines)(If possible the butt lines too)

I tried searching the internet for the station number and couldn't find what I'm looking for. Or am I looking at the wrong place to find it? Where to find the number if you don't have access to the aircraft maintenance manual?

For the wing tip station , just divide the wingspan by two and multiply by 12.  The stations are in inches.  For a 747 with a 195' 8" wing span, the tip station is 195.66 divided by 2, times 12 = 1173.96, so the tip will be Station 1174.
For X and Z you need to know where the datum point is longitudinally and for the X axis, and what the waterline is that defines the Z axis.  Waterline is often the cabin floor.  X datum on a jet is often the forward pressure bulkhead surface.

can you give an example position for the water lines and butt lines

Look up the SE post What Is The Coordinate System Used On Aircraft, from about 3 years ago.

Strictly speaking, wouldn't Station 1174 be one twenty-fifth of an inch beyond the wingtip?

This is incorrect as wing station on a swept wing aircraft generally follows a line parallel to the sweep on the leading edge starting at BL0.

I wish I had the chart of this from Boeing’s MDF on the 747, but a good estimate might be as follows.
A Boeing 747 has a wingspan of 195 ft 8 in and a LE sweep of 37.5°.
Therefore:
Span (in): 2348 in
So wingtip lies on BL 1174.
The wing station uses a different coordinate system for swept wing aircraft which is parallel to the wing LE or similar datum.  Using the wing LE as a datum, this gives:
1174/cos(37.5°) = 1479.79
So the wingtip would be at WS 1479.79
NOTE: this is a reasonable estimate and not to be taken


text:
Can I listen to control tower frequencies on a ham radio legally
Is there a frequency I can tune into to listen to airport I’m in Durham by RDU AIRPORT and would like to listen in on a ham radio only legally

Are you asking about USA rules?

Aviation communications frequencies are typically 118.0 to 137.0 MHz. If your radio can receive those frequencies, I see no reason why you can’t listen.

In North America, just buy an air-band radio and listen to Raleigh-Durham tower all you like, or if your ham unit receives the aviation VHF frequencies, do that.  Or find it on LiveATC.net  It's only illegal to broadcast without authorization, not listen in.

A list of RDU frequencies is here.

Note that many ham radios are capable of receiving those frequencies but don't have an AM demodulator, only FM or SSB.

Also, while it doesn't apply to the OP in the US, for completeness it should be noted there are some countries (e.g. UK) where even listening to a radio broadcast is illegal if you aren't the intended recipient.

@StephenS Same for Germany: it's illegal to listen to ATC radio as long as you are not involved somehow. If you wander around in typical planespotter areas and wear earplugs, chances are that you are being asked what you listen to.

Thanks. Added North America reference.


text:
How do I know how to describe my position on the airport when I contact ATC?
When asking for taxi clearance, a pilot must include his location when contacting ATC. However, I'm not quite sure exactly how to state your position in the airport.
For example, I've heard some pilots say something such as "Ground, N123DB is southside by the tower, requesting taxi clearance," but I've also heard something like "Ground, N123DB is at transient parking, requesting taxi clearance." How do you know your location in the airport?
Obviously, I can look at an airport diagram and find out where I am, but how do I communicate this using proper terminology to ATC? Is it standardized?

If you're based at the airport, you should know which FBO you pay, no?  If you landed there, the tower would have directed you to an FBO or transient parking.

There isn't really an official protocol, beyond the conventions everybody uses out of habit.  Just pick the most prominent landmark, building or chart-labeled zone you can find or think of.  The controller knows all of them so as long as it's not something like "next to a light pole", he/she will figure it out, and if not, they'll ask for clarification.
If the airport has an area designated "transient parking" on the airport chart, use that.  If you're on a ramp area close to the entrance to taxiway Alpha, you could say "xxxx on the ramp near Alpha".  If you're on a ramp in the hinterland somewhere near some hangars, pick the nearest building with a business name associated with it, like "xxxx by Standard Aviation...", or "xxxx by the Shell fuel pumps", whatever.  Use common sense and don't overthink it.

As a matter of course, I make it a habit to wait to call for taxi clearance until I am in view of the tower, facing the movement area, with my beacon and taxi lights on, and my engine running. If I can see the tower, more than likely they can see me. Being in a position and condition to taxi will make it easier for ATC to distinguish my plane from the others. If they still have issues distinguishing the plane, giving ATC the aircraft’s current cardinal direction heading may help.
Another good habit to make it easier for ATC (and any other pilots and personnel moving around the ramp) is to replace the country of registration designation with your plane model. Instead of saying “N”, say “Skyhawk”, “Archer”, or whatever model you are flying. According to AC 90-66B:

Paint schemes and color or style descriptions may be added to the use
  of the aircraft call sign and type, but should not replace type or
  call sign. For example, “MIDWEST TRAFFIC, TWIN COMMANDER FIVE ONE
  ROMEO FOXTROT TEN MILES NORTHEAST” or “MIDWEST TRAFFIC, FIVE ONE ROMEO
  FOXTROT TWIN COMMANDER TEN MILES NORTHEAST.

And, just because it is an airfield without ATC, doesn’t mean it is not a safe general practice to announce your movement in the movement area over CTAF.
In general, you are allowed to move the plane up to the point right before entering the movement area in the GA designated area of the airport prior to getting your clearance. Then, give ATC your position as a general landmark. If there is only one FBO, you can just say the “FBO ramp”. If the FBO has a name, use the name in place of “FBO”. If your position is at the fuel farm, say the “fuel farm ramp”. If you are at a school, use the school name. Same with a mechanic/technician shop. In place of knowing your exact position on an airport diagram, these are the places you will most frequently visit as a transient GA pilot. You can also use the closest taxiway intersection.

"Then, replace the entire tail-number with the model and color." The FAA says not to do this. See 10.3.1 in AC 90-66B

@reirab - Thanks for the correction.

Just for completeness, there are airfields which require permission to start.

@Dan - Interesting point, Dan. I’ve never had that issue in the Class Ds that I’ve been to. None of the very few Class B or C’s I’ve been to required it either for GA piston-powered prop planes. Although, I know it may be standard for turbine-powered aircraft at the commercial terminals. I would be curious to know which airports require it for my kind of traffic.

@DeanF. Permission to start is standard ICAO; the FAA grants it by default unless the ATIS (or ramp owner) says otherwise.


text:
Is (or was) it acceptable to throttle up for takeoff before being aligned with the runway center line?
30 years ago I was on a flight from Spain to Brussels and when we were heading to the runway for takeoff, the commander opened full throttle to the engines while we were still some 60º away from being straight on the center line. At the same time he said loudly over the cabin loudspeakers "¡Nos vamos!" (Let's go!).
Well, a psychiatrist on board said: "A psychopath, a complete psychopath!". And Gerald L Klerman, MD once told me that the FAA was concerned about finding a way to detect a manic pilot before takeoff.
Was the pilot dangerously irresponsible, or was it an acceptable way of handling an airplane?

No objective test (like a blood analysis) exists yet that may identify a manic individual. Psychiatric diagnosis is based on observation and interviews, and is necessarily subjective...

Acceptable to whom? Passengers probably not. The airline or FAA maybe.

Functional Magnetic Resonance Imaging, SPECT, and other techniques as Computerized Analysis of EEG may detect differences between a normal and a manic or psychotic brain even when behavior is 100% normal. Some Air Force Units interviewed pilots in a regular schedule 'to detect stressors', but this is a bit transferring the command line to the medical corps. The doubt about if this way of taking off is within allowances remains unanswered in full. Thanks, regards. Salut +

I was on board, and besides having some fun, It wasn't different to me from any other usual flight. I didn't feel in danger

I would ask how you knew it was full throttle?  What kind of airplane?

Engines take a while to spool up to full power, so pushing throttles forward while in the turn means they will be up to full power by the time you're aligned.

It's unclear what exactly your question is here... while it's an interesting story, you may want to edit to focus on your question, whether it's the psychology or piloting side of this.

30 years ago, being gay was officially (according to DSM) a psychiatric disorder, and masturbation was subject to cure in Switzerland. Your passenger doctor was possibly thinking that too, so...

It is fairly common for some engine power to be applied before being fully aligned with the runway, in a rolling takeoff.

In the 90's when I'd jumpeat on cargo flights, if they had takeoff clearance when they entered the runway they'd push the throttles up while still turning. They didn't waste time. Clear the runway for the next plane. Then again, they didn't have any passengers to scare, aside from me. Nobody ever shouted "YeeHaw" or anything. That makes all the difference

Possible duplicate of Are rolling takeoffs now more common than powering up while holding on the brakes?

Pilots in any size aircraft may sometimes be given an instruction from ATC such as "... Cleared for immediate takeoff ..." which means that the pilot is expected to execute the takeoff as quickly as he/she can safely do so.  That may involve applying noticeably more power than normal for the roll from the taxiway out to turn and line up with the centerline of the runway, to keep the speed up and get off the ground as soon as possible.  For example, there may have been an aircraft on final approach for the same runway and the air traffic controller wanted to be sure to maintain ample separation from the departing aircraft.  So unless you were in the cockpit hearing the radio communications and seeing what the pilot may have seen in the approach corridor, it's difficult to say for sure whether the pilot was hot-dogging or was just wasting no time getting out of the way of arriving traffic as soon as he could.
But on the other hand ... announcing to passengers "Nos vamos" while hitting the throttle in the taxi turn out to the runway centerline ... at best, that doesn't exactly sound like what a cautious and conscientious airline pilot would choose to be doing in that moment!
With two pilots in the cockpit it is not unusual for one to do the radio communications while the other manipulates the controls to fly the airplane.  Those words could have been quite fine for one pilot to say to another in the cockpit intercom as emphasis.  Maybe the pilot only meant to do that but mistakenly transmitted it to the passenger cabin instead; in which case that would have been an unfortunate and unsettling error although not an especially dangerous one.
Although I haven't done such a report myself (because thankfully I don't recall being involved in such an incident), if you observe an airline pilot doing something you consider very dangerous or inappropriate I'm pretty sure the airline would want to hear directly from you about it with details such as flight number, date and time of the incident, so they can investigate.  We can each do our part to keep flying safe!


text:
What were the make and model of the engine that failed in flight Southwest 1380?
Regarding the tragedy of Southwest 1380 flight on 2018-04-17 involving an engine failure, what company manufactured that engine, and what engine model/type was it?

Dear Down-Voter, please leave a criticism along with your vote. I do not understand how a Question deserves 2 down-votes with an Answer that deservers 2 up-votes.

Perhaps you could add some details about your research so far.  I suspect that that is the reason for the down-vote.  (Yes I understand that you answered your own question but SE typically likes for you to show your previous research)

According to this article published on news.com.au:

Engine model is CFM56-7B, debuted in 1997.
Manufacturer is CFM International, jointly owned by General Electric of the United States and Safran Aircraft Engines, a division of Safran of France.

More specifically, AirFleets.net reports:

Engine model: CFM56-7B24
Plane: Boeing 737 Next Gen, variant group 737-700

More info on the flight
https://www.ntsb.gov/news/press-releases/Pages/NR20180503.aspx
NTSB Issues Investigative Update on Engine Failure
5/3/2018
WASHINGTON (May 3, 2018) — The National Transportation Safety Board issued an investigative update Thursday for its ongoing investigation of the fatal, April 17, engine failure on Southwest Airlines flight 1380.
The Boeing 737, powered by CFM International engines, experienced a failure of the left CFM-56-B engine after departing New York’s LaGuardia Airport. The engine experienced a failure of a fan blade, which resulted in the loss of the engine inlet and cowling. Fragments from the cowling and engine inlet struck the fuselage, causing a rapid depressurization. The crew conducted an emergency descent and diverted to Philadelphia International Airport. There were 144 passengers and five crewmembers onboard.  One passenger suffered fatal injuries and eight passengers suffered minor injuries. The airplane was substantially damaged.
https://www.ntsb.gov/investigations/PublishingImages/DCA18MA142-update-fig1.jpg
(In this NTSB photo-illustration, damaged components of the left engine are identified as viewed from the inboard side of the CFM-56-B engine. During climb out following departure from New York’s LaGuardia Airport, the engine experienced a failure of a fan blade which resulted in the loss of the inlet and cowling. Almost the entire inner and outer barrels of the inlet cowl were missing as were the forward and aft inlet bulkheads. NTSB Photo-illustration)
According to the investigative update, the aircraft’s maintenance records indicate, the fan blades were last overhauled 10,712 engine cycles before the accident. At the time of the last blade overhaul (November 2012), blades were fluorescent penetrant and visually inspected.
The investigative update includes a summary of the interviews conducted by the NTSB with the captain and co-captain, the three flight attendants, and a SWA employee in the cabin.
The cockpit voice recorder group has completed a draft transcript of the incident. The CVR transcript will be released when the public docket is opened.
The information in the update is preliminary and subject to change as the NTSB’s investigation progresses. Analysis of the accident facts, along with conclusions and a determination of probable cause, will come at a later date when the final report on the investigation is completed. As such, no conclusions about how the incident happened should be drawn from the information contained within the preliminary report.
The incident marks the first fatality involving a U.S. registered commercial passenger air carrier since the 2009 Colgan Air flight 3407 crash near Buffalo, New York.
The full investigative update is available online at https://goo.gl/bJCGdo


text:
If you depressurize an aircraft at FL340, will the temperature inside fall to match the temperature outside?
Assuming you’d have an oxygen mask on before hand, and you depressurized the aircraft at FL340, would the inside and outside temperatures quickly become the same?

It depends on your definition of "quickly", and whether or not you continue pumping hot air, (albeit at significantly lower pressure) into the cabin.

@BenCrowell Yes, that's exactly what it means. It's a pressure altitude of 34,000 feet.

Are you thinking about the worst greek air disaster?
https://en.wikipedia.org/wiki/Helios_Airways_Flight_522

This depends entirely on how you depressurized it.
Depressurizing the aircraft by fully opening the outflow valve will lower the temperature somewhat, but will not bring it to that outside.
The expansion process will be closest to free (Joule) expansion, which causes only small decrease in temperature, not an adiabatic one that corresponds to the atmospheric lapse rate. And while some energy will be lost through the air's initial expansion as it escapes, it will quickly be replaced by new warm air coming in through the packs (cabin pressurization and air conditioning system).
That air supply is quite reliable, as it's bled from engines at about $200\ \mathrm{^\circ C}$ – it then needs to be air-conditioned so as not to roast the passengers. The packs will automatically maintain set temperature, putting less effort into cooling the air if the cabin gets too cold.
If you also disable the engines, so no new air can come in, the airplane will lose some heat. Still, in all other regards, the fuselage will remain a well-insulated vessel with some heat sources on the inside. Also, the less-dense air is much less effective at heat transfer, and has much less heat capacity, so it will get chilly, but the passengers aren't going to freeze to death or even get a frostbite.
The heat capacity of air at ambient pressure will be about $280\ \frac{\mathrm{J}}{\mathrm{m}^3\cdot\mathrm{K}}$. A 737 encloses about $200\ \mathrm{m}^3$, giving a total of $56\ \frac{\mathrm{kJ}}{\mathrm{K}}$. For comparison, the plane's passengers have a specific heat capacity of $3.5\ \frac{\mathrm{kJ}}{\mathrm{kg}\cdot\mathrm{K}}$, giving, for 120–160 of them, about $40\ \frac{\mathrm{MJ}}{\mathrm{K}}$. So a $\sim70\ \mathrm{^\circ C}$ one-time drop in air temperature can technically match the outside, but it can only cool the passengers by at most $0.1\ \mathrm{^\circ C}$.
In practice, the cooling won't be instant, and it has to compete with heat exchange with the still-warm interior. Passenger bodies producing $12{-}18\ \mathrm{kW}$ of waste heat (at rest) will also restore cabin air temperature by $\sim1\ \mathrm{^\circ C}$ every 4 seconds. The larger the hole, the lower the temperature minimum that will be reached. With a broken window, the effect of this one-time expansion heat loss will have been mostly undone before anyone notices it, amidst the chaos.
Tearing the top of the fuselage off, on the other hand, will most definitely let the passengers feel the cold outside. But it will be the powerful wind blowing in, not the air leaving the airplane, that will chill its interior.
Breaking a single window or making a lot of bullet holes (really a lot - it will take a crate of ammo to overcome the packs' air inflow) is about the same as fully opening the outflow valve. It will produce some cooling effect, but it will definitely not bring the interior to the outside temperature, as the cooling effect is one-time, and will be rapidly compensated for.
This kind of event has happened a few times in aviation history. It has caused some fatalities – a person sitting right next to the broken window has been killed by the mechanical force of the escaping air. No one has been frozen to death, not even in the Aloha Flight 243, which represents about the worst possible case for depressurization (which still leaves survivors and not just a debris field).

@Bianfable The plane was turned into a landaulet, with winds free to ravage the interior, and getting scooped up by the remaining part of the fuselage. It's as bad as it gets while still allowing the plane to land (thanks to the cockpit staying enclosed).

What's a "pack(s)"? And can those, or any other part of a plane's HVAC system be run on the APU? And can the system provide heat with the engines off?

@Mazura Integrated or packaged aircon system. And from the diagrams here, it looks like yes, the APU can supply them, though likely not enough for full performance.

@SomeoneSomewhereSupportsMonica, if the APU is running, it can feed the packs, but most APUs won't run at cruise altitude.

Assuming the cabin is pressurized to a pressure equivalent of that at 8000ft, the initial pressure is on board is $P_1$ = 75262.4 Pa, and the temperature is T1 = 20ºC = 293.15K
At FL340, the outside pressure is $P_2$ = 24999 Pa.
Assuming we are talking about rapid decompression, there will be no significant heat transfer into or out of the gas during this process. We can thus approximate the temperature by using the laws of adiabatic cooling.
$P^{(1-\gamma)}T^\gamma = $ constant
Therefore:
$T_2 = \sqrt[\gamma]{\frac{P_1^{(1-\gamma)}T^\gamma}{P_2^{(1-\gamma)}}}$
With $\gamma$ = 1.4 for air.
Filling in the numbers will give $T_2$ = 213.96 K = -59.2ºC
The normal temperature at FL340 is about 222.8 K or -52.4ºC
After a rapid decompression, the temperature on board will thus be slightly below the outside temperature.
This sudden loss of temperature will cause moisture in the air to condensate into fog.
Since all the interior mass of the cabin is still at 20 degrees, the temperature will quickly rise again and the fog will disappear.
Here is a video of a rapid decompression in a pressure camber.
Note the fog, and note how quickly the person passes out.

Excellent explanation that caters to all levels of knowledge!

Keep in mind that this is free expansion, as gas is not doing work against a piston. In free expansion, temperature change is minimal. A smaller hole is not completely free expansion, but much closer to it than it is to a heat engine cycle.

Note that the fog dissipates almost as quickly as it appeared though...

@JanHudec I guess that is because the fog is very good at catching IR radiation. Since the walls don"t cool down, there is plenty of heat transfer into the fog and since there is very little mass in the air, it warms up very quickly again.

@Therac Rapid decompression in an aircraft is no free expansion, there is no vacuum outside. Instead the outside air has quite some pressure and air inside the aircraft does the work of pushing that away.

The part I noticed in that video was how much difficulty the guy had getting his mask on. He knew it was coming. He had the calm reassurance of someone standing right there already fitted with O2 who he knew would step in to help him and he couldn't get the strap over his head. It took the helper several tries, too, while the test subject started to lose consciousness. Pretty scary! People, put your own mask on before trying to help anyone else, lest you join the dead!

@DeltaLima, it isn't. IR cameras are used to see through fog.

More or less...
For gamma = 1,4, an adiabatic expansion from 1013 hPa to 226 hPa will cause an initial temperature of 20ºC = 273K to drop to 191 K.
The Standard Atmosphere temperature for that altitude is approx. that...

Are you sure the expansion would be isentropic?

@xxavier, Are you saying that the standard atmospheric temperature at FL340 is +20C?  If not, would you please clarify?

@MichaelHall Pretty sure he is assuming the cabin temperature to be 20°C but forgot to add the 273.15K to make it 293.15K in the cabin at the start of the expansion.

Yeah, but he goes on to say "the standard... is approx that".  Meaning approximately equal.

@pericynthion the OP does not specify, so lacking further nuance it is the only meaningful assumption, since the opposite possibility from a thermodynamic perspective would be an isothermal process, would it not?

@MichaelHall I read that as 191K, which is indeed close to the ISA temperature at 12km.

This holds only if no new air is coming in from the packs and if the passengers and the airplane aren't producing any heat. The heat capacity of that low-pressure air is tiny.

OK, let's get the numbers and units of measure defined and accurate.  191 degrees kelvin, (presuming that is "K"?) is -82C or -115F.  This is not 20C, nor is it the standard atmospheric temperature at 34K feet which is roughly -50C or -60F.  Please expand and clarify this answer.

The expansion will most definitely be isochoric, not adiabatic. Adiabatic expansion happens in a sealed cylinder, when the gas is producing work by acting against resistance. Air expansion from a tear in a container is going to produce Joule expansion, which results in no cooling with ideal gases and only a bit of cooling with real gases.

@MichaelHall ok, to straighten it out, it's either degrees Celsius or Kelvins (which are not degrees), and what I believe the answer says is, air with $\gamma$=1.4 at 273K would cool to 191K during an adiabatic expansion, which is rather close to the 220K at 34kft ISA. Therac: oh, yeah, that one... I had a feeling I was forgetting something.

Thanks for clarifying, I did not convert 220 Kelvin so 191 is closer than I realized.  Having said that, pilots and most lay people don't deal with Kelvin.  I am reasonably intelligent and can appreciate scientific explanations, but answers should be tailored to a wider audience.  And I don't know what "gamma = 1,4" means either...  For that reason I am downvoting for now.

@Therac, Joule expansion assumes expansion into a vacuum, so no work is done by the gas. That is not the case here; the pressure at FL340 is lower than at sea level, but nowhere near vacuum.

@DeltaLima True. Thinking about it, this is neither the Joule process nor isentropic expansion. The case is actually a lot more complex than just using one linear formula, it's not any one simply-modeled process. The truth will be somewhere in between, the air will cool somewhat, but it's expanding against very little resistance, just equalizing the pressure on two sides of a wall.

The air in the cabin is not 1013 hPa, it is only 750 hPa.

@Therac: the air remaining inside the fuselage is doing work pushing air through the hole.  The air going through the hole is expanding into much lower pressure.  Analogy: a CO2 fire extinguisher blows cold CO2 that expanded from a much higher pressure.  The tank of the extinguisher also cools off some, I think?  I also considered a propane tank for a BBQ or camp stove, but I think in that case some of the cooling is from liquid propane boiling to maintain constant vapour pressure in the tank so it's not a good analogy.  Heat of vaporization is different from ideal or real gas expansion.


text:
How do helicopters avoid detection from enemies by using IR suppressors?
no IR suppressor
 IR suppressor
All I know is that it blends the hot air before releasing it How does an IR suppressor help an aircraft avoid detection from a missile? Wouldn’t the entire helicopter show up on the IR?

An IR sensor detects objects that are at a higher (or lower but that's not how missiles work) temperature than the surrounding environment, most of the helicopter won't be that much hotter or cooler than the air around it, so wouldn't distinguish it much unless you get very close. Jet engine exhaust is much hotter than the surrounding environment, so it shows up very clearly to an IR sensor from far away.
A suppressor diffuses hot exhaust into a larger air mass, lowering the temperature of the exhaust compared to the surrounding air before the sensor can see it. Lower temperature means less heat for a sensor to see.  A suppressor also makes the infra-red picture fuzzier, i.e. less of a distinct point. The lower temperature and fuzzier image decreases the effective range for a sensor, meaning it would have to be closer to detect it. Suppressors often deflect exhaust, pointing it away from where a sensor would be expected to read, or shield the exhaust.
Suppressors don't prevent an IR detection in the same way that stealth doesn't prevent radar returns, but a suppressor means you need to get closer.

Larger volume of air I think you mean, not surface area?  Or perhaps "mass" of air, because number of jiggling molecules is proportional to mass even at non-constant temperature.  (And that's what matters for temperature of the mixture).  Although volume around the chopper would be what matters for making it fuzzy, although from any given direction you're seeing the cross-sectional area of the parts that are "deep" enough to see.

That's a good point @PeterCordes, I've rephrased to say "air mass" instead as you suggest.

The key is in the spreading around bit, right? A can of paint is not going to provide the same intensity on a square mile as it would on a square foot, while there's still the same amount of paint.

That works as an analogy @Mast. Another way to say it is imagine you have 1 100 watt light bulb or 10 10 watt bulbs spread over a couple of square meters of space, which are you going to see from a distance?

To add to GdD's fine answer:
The environment provides plenty of different heat sources for the missile to see. To get a target lock, the "signature" of the heatsource has to be of quite a specific kind. Anything simply hotter than the surroundings will not be sufficient. The specifics of the way a missile lock is aquired and maintained is of course classified, but as the example in the picture shows, a quite simple contraption quite effectively  reduces the threat of IR missiles.
It mixes the exhaust with cooler air as you described, directs it away from the probable direction of the threat (surface to air) as GdD described and in addition to those, the rotor downwash blends the exhaust gasses even further to make the IR signature fuzzier.

The specifics are somewhat unknown, but I think it's safe to say the missile is looking for a bright beacon of heat compared to the background.  Something warm or even somewhat hot is ignored - it needs to be very hot to get a lock, and any aircraft without countermeasures will provide that very hot exhaust.

@JPhi1618 On older missiles (Sidewinder AIM-9 circa mid 70s comes to mind) I have seen the seeker track a person a few hundred feet away when fitted for a training mission (only the seeker section of the missile was loaded on the pylon). There was also an amusing event of a live firing that was confused by two flares and the missile went between them.

Missiles may also expect the IR source to be steady. IR jammers like the AN/ALQ-144 contain a powerful IR source that is occluded by spinning vanes.


text:
Can a CFI provide endorsement training to non-US citizens without TSA approval?
Does a CFI need TSA approval to provide endorsement training to non-US citizens, such as the complex, high performance and tailwheel endorsements laid out in 14 CFR 61.31?
Recurrent training is exempt from TSA approval, however training for an endorsement isn't recurrent because it doesn't have to happen again. And it includes training in an aircraft, which usually requires TSA approval.
Some places such as AOPA suggest all of 61.31 is exempt:

He/she is seeking recurrent training, such as a flight review,
instrument proficiency check, or flight training listed under 14 CFR
61.31

But the TSA only suggests that 61.31(g) is covered:

High Altitude Training (HAT)  14 CFR Part 61.31(g) - Type rating
requirements, additional training, and authorization requirements.

If only 61.31(g) is exempt then only high altitude endorsement training is exempt, and TSA approval is required for complex, high performance and tailwheel. Is that accurate?
Government references are highly appreciated.

Assuming the crux of this question is about the need for TSA clearance for the training then the answer can be found in the FAQ section of the flight school candidate website under the question;  When is a flight student exempt from the requirement to undergo a TSA security threat assessment?
You will see a table with some exemptions including the 14 CFR §61.31(g) exemption. The table is prefaced with the statement;

Other training activities that do not require notification to TSA are
  exempt only if the candidate holds an FAA stand-alone Pilot
  certificate

In other words a pre-existing FAA pilots license acts as some what of a verification and you do not need to be re-verified.
Interestingly only 14 CFR §61.31(g) is exempt so presumably only the high altitude sign off can be obtained under this exemption the rest of 14 CFR §61.31 does not fall under it. I would say the AOPA site is incomplete in their information.  A CFI may provide training for 14 CFR §61.31(g) without TSA authorization but if the student is seeking training on any other endorsements under 14 CFR §61.31(g) then they must get cleared by the TSA.

So, what do CFI's currently do?  Do they provide the training for a complex endorsement if a current / valid pilots license is provide?  Or do they re-initiate TSA checks?
What is the current industry practice in these cases?

@chup The regulations would prevent them from providing training for a complex endorsement until such a time as all TSA paperwork is sorted. If you can prove you have been cleared by the TSA or the flight school clears you, you can train. Its also important to stress that it must be an FAA Issued license

Thank you for all the insight I really appreciate it.  Given that a cfi and a flight school are both flight schools, do you know where the regs state that if the flight school I work at clears it, I can train?

@chup do you work at a US flight school are you legal to work in the US? (this likely changes things). I would think that both a flight school and/or CFI can submit the paperwork but ultimately as the PIC the CFI is the last decider.

Person has current valid pilot certificate, Flight school says person is good to instruct for complex endorsement.  Complex endorsement is not on the list here:  https://www.flightschoolcandidates.gov/home.  So how is it safe to provide that instruction?

@chup it’s not legal, Saftey is not relevant to this regulation, and the flight school simply may not know the regulation however it sounds like that person has already passed the background check required if they have an FAA issued pilots license and it’s current.

As far as I can see you don't need TSA approval for any of the 61.31 endorsements because they don't meet the TSA's definition of "flight training" that they clarified in a letter to AOPA:

“Flight training” is defined in 49 CFR 1552.1(b) as “instruction
received from a flight school in an aircraft or aircraft simulator.”
TSA interprets this definition to include only that training that a
candidate could use toward a new airman’s certificate or rating.

Endorsements are neither certificates nor ratings. All the flight training events that do require TSA approval - initial, instrument, multi-engine and type ratings - do result in another certificate or rating.
As for why the TSA specifically calls out 61.31(g), I suspect that whoever put together the FAQ didn't pay attention or just didn't think that other endorsements were relevant. I can't find any other document or source where the TSA calls out the high-altitude endorsement specifically, or even mentions the other endorsements. If they really insisted on approving tailwheel training I'd expect to find some references easily, if only because AOPA and EAA would have kicked up a fuss by now.

Well, I really appreciate the effort of clarification here.  Tragically I believe that the federal gov has once again left things so ambiguous that, if it suited their needs, they'd coerce TSA-2004-19147-0226 into what they desire.  For example, consider the spirit of the following paragraph in that doc that contains:

continued:
"TSA believes that the requirements of the Interim Final Rule should be limited to this type of training because it allows individuals without any training to learn how to operate an aircraft, and allows pilots who already have the skills to operate an aircraft to gain new operating skills.  Tailwheel, Complex and High Performance are all "new operating skills"
Wouldn't it be nice if they just said "The TSA doesn't care about endorsements"


text:
Do TSA regulations allow CFIs to start training non-citizens before the TSA has approved their training request?
49 CFR 1552.3 says (emphasis mine):

(4) TSA has informed the flight school that the candidate does not
pose a threat to aviation or national security, or more than 30 days
have elapsed since TSA received all of the information specified in
paragraph (a)(2) of this section.

This one implies we can't train until we hear back from the TSA for aircraft that are in "Category 1—Regular processing for flight training on aircraft more than 12,500 pounds".
However, the section on "Category 3—Flight training on aircraft 12,500 pounds or less" says:

(4) The flight school begins the candidate's flight training within
180 days of the date the candidate submitted the information required
under paragraph (a)(2) of this section to TSA.

So that tells me that as long as the information is submitted, we can begin training a non citizen immediately (for less 180 days).  What is the point of this?  Where is the security?  Is this correct? Or is it just another confusing regulation?
What is the current industry practice? Do CFIs provide the training in this situation? Or are more TSA checks initiated?

Immediately after your quoted emphasis it states "or more than 30 days have elapsed"  So if the TSA has not responded within 30 days, you're good to start teaching them as long has 30 days have passed.  Right?

This is addressed in the AFSP Candidate FAQ, which confirms that you can start training in category 3 as soon as all information has been submitted:

How long should I expect to wait after I have submitted my training event request?
[...]
Candidates in Initial, Instrument, and Multi-Engine training (category
3) may begin training as soon as AFSP receives all required
information, including the candidate's passport, fingerprints, the
fee. You and the provider will be notified once AFSP receives the
fingerprints and you have been granted Permission to Initiate
Training.

That's also what the regulation says, but the FAQ may be a little clearer.

Yes training can be provided for aircraft under 12,500 LBS
Category 1 and 2 apply to training in aircraft over 12,500 LBS. Category one is the standard process for application.

(a) Category 1—Regular processing for flight training on aircraft more
  than 12,500 pounds.
A flight school may not provide flight training in
  the operation of any aircraft having a maximum certificated takeoff
  weight of more than 12,500 pounds to a candidate, except for a
  candidate who receives expedited processing under paragraph (b) of
  this section, unless—

Category 2 does lay out a process for expedited applications that has some time requirements but section (iv) notes that you still must hear back from the TSA before training begins.

(b) Category 2—Expedited processing for
  flight training on aircraft more than 12,500 pounds.
(1) A flight school may not provide flight training in the operation of any
  aircraft having a maximum certificated takeoff weight of more than
  12,500 pounds to a candidate who meets any of the criteria of
  paragraph (b)(2) of this section unless—
(iv) TSA has informed the flight school that the candidate does not pose a threat to aviation or national security or more than 5 days have elapsed since TSA received all of the information specified in paragraph (a)(2) of this section.
(v) The flight school begins the candidate's flight training within 180 days of either event specified in paragraph (b)(1)(iv) of this section.

Category 3 applies only to aircraft of 12,500 LBS or Less and section 4 does indeed allow you to start training so long as it beings within 180 days of your paperwork being submitted.

(c) Category 3—Flight training on aircraft 12,500 pounds or less. A
  flight school may not provide flight training in the operation of any
  aircraft having a maximum certificated takeoff weight of 12,500 pounds
  or less to a candidate unless—
(1) The flight school has first notified TSA that the candidate has
  requested such flight training.
(2) The candidate has submitted to TSA, in a form and manner
  acceptable to TSA:
(i) The information required under paragraph (a)(2) of this section;
  and
(ii) Any other information required by TSA.
(3) The flight school has submitted to TSA, in a form and manner
  acceptable to TSA, a photograph of the candidate taken when the
  candidate arrives at the flight school for flight training.
(4) The flight school begins the candidate's flight training within
  180 days of the date the candidate submitted the information required
  under paragraph (a)(2) of this section to TSA.

So for aircraft over 12,500LBS you must hear back from the TSA in some capacity before training begins. While for aircraft under 12,500LBS you can start your training as soon as the paperwork is submitted.

I didn't miss any of that.  It is just very confusing / surprising that the training can be given at all before a confirmation of cleared is received.  Thanks

@chup This has largely to do with/as a result of, the September 11th attacks, I think that the notion is that less damage can be done in/with a small aircraft.


text:
Does a CFI have to be a CFII to fly with a student in IMC?
A CFI wants to fly with a student under the following conditions:

CFI has ASEL pilot cert with Instrument Rating
CFI has ASEL Instructor cert with NO Instrument Rating
CFI is current in all regards
Flight will be IMC
The Training will not count toward a rating
Will be logged with dual given and actual intruments

"The training will not count toward a rating" how do you outline that in the log book?

who cares?  that's a separate problem.

No, a pilot with CP-ASEL-IA and CFI-ASE who is instrument current can take a student into actual IMC, and can even log it in both logbooks as dual training if the instruction is on the area of operation described in FAR 61.107(b)(1)(ix) "Basic Instrument Maneuvers" (etc) because that AOA is towards a private pilot certificate. However, this would be a Dumb Thing to Do because a CFI with no -I does not have any training flying instruments from the right seat, which is a skill that takes quite a bit of practice.
The thing that a CFI-I allows a person to do is to provide training on the areas of operation in FAR 61.65 towards an instrument rating.

The lack of CFI-I does not necessarily mean the CFI has no experience flying IFR from the right seat, just that he hasn't taken a checkride on it. Many don't, of course, but many do.


text:
Is it legal to fly without a transponder?
Everything is legal / airworthy.
Except:
Transponder is installed.  It does work.  It has NOT been inspected in any time frame that would show it is properly maintained.
Flight is
Golf, Echo, Delta < 2500 AGL
Can I shut off the transponder and fly legally?

Are you flying in controlled airspace?

I already stated where the flight will be.  E is controlled.
I love how all FAA questions are 50% yes, 50% no

"Flight is Golf, Echo, Delta", you likely wanted to write "airspaces used are classes D, E and G" but you had not enough time, given that you have no time to select helpful answers.

I still dont have a helpful answer.  1/2 contradict the other 1/2

@chup this is very complicated. Take a look at FAR91.225. You're probably ok with regard to transponder issue, but if your aircraft uses your transponder to transmit ADS-B Out then you might be in violation of 91.225(f). I'll type up an answer for you when I get a chance.

Yes, you can in the US in Class D, E & G airspace according to 14 CFR 91.215. You will need to placard the transponder INOP, and make a note in the aircraft logbook. But, you must stay out of any Mode C Veils, and further than 30 miles from Class B airports. Also, stay below 10,000 feet MSL unless that means you are below 2,500 feet AGL. However, you can request a deviation to 91.215 from ATC in advance.

This is a complicated issue because technically with regard to the transponder there are areas where it is not required under 91.215(b), namely Class G and certain altitudes and places in Class E.
However, in the same section in subpart (c) of 91.215 it says

"... or in all controlled airspace, each person operating an aircraft
equipped with an operable ATC transponder maintained in accordance
with 91.413 shall operate the transponder."

So subsection (c) puts you right back at if you got it you have to use it. Unless its inoperable or if it was not inspected within the preceding 24 calendar months in accordance with 91.413, then you are prohibited from using the transponder.
To complicate matters now we have ADS-B Out requirement under FAR 91.225(f) which states

"...each person operating an aircraft equipped with ADS-B Out must
operate this equipment in the transmit mode at all times...."

The reason this is important is that many installations transmit ADS-B Out information through the transponder, so if the transponder is turned off, you will not be able to comply with FAR 91.225(f).
There are two ways to transmit ADS-B Out information, one is 978UAT and the other is 1090ES. I believe 1090ES is the method that uses Mode S Extended Squitter transponders and if this is the method your aircraft uses, turning off the transponder may turn off the ADS-B Out information in violation of 91.225(f).

Most of the Airspace specified in paragraph (b) of 91.215 is: B, C, Mode C Veils, and the airspace overlying B & C.

Welcome to Aviation.SE! Answers here should be complete and stand on their own. You can edit your answer to add more information.

NO.
The FARs are pretty clear about this. If it is installed it must be inspected within 24 months—otherwise you can’t fly (with some exceptions e.g. ferry permit). If it passed inspection, it must be on. If it fails then you may fly with an inoperative transponder (with some exceptions and notifications as described in the FAR). You can’t turn it off and fly legally.
In your case you cannot fly because you have an operable transponder that has not been inspected (and passed) in the previous 24 months and you want to fly in controlled airspace.
§91.413   ATC transponder tests and inspections.

(a) No persons may use an ATC transponder that is specified in
91.215(a), 121.345(c), or §135.143(c) of this chapter unless, within the preceding 24 calendar months, the ATC transponder has been tested
and inspected and found to comply with appendix F of part 43 of this
chapter; and

§91.215   ATC transponder and altitude reporting equipment and use.

(c) Transponder-on operation. While in the airspace as specified in
paragraph (b) of this section or in all controlled airspace, each
person operating an aircraft equipped with an operable ATC transponder
maintained in accordance with §91.413 of this part shall operate the
transponder, including Mode C equipment if installed, and shall reply
on the appropriate code or as assigned by ATC, unless otherwise
directed by ATC when transmitting would jeopardize the safe execution
of air traffic control functions.
(d) ATC authorized deviations. Requests for ATC authorized deviations
must be made to the ATC facility having jurisdiction over the
concerned airspace within the time periods specified as follows:…

91.413 No persons may "use"
91.215 ..."maintained in accordance with"
I'm leaning to the side of it being acceptable.

@chup but look at 91.215 it says each person with an operable transponder shall operate the transponder.

-1. As you say: each person operating an a/c equipped with an operable xpdr maintained in accordance with 91.413 shall operate that xpdr in all controlled airspace. If the operable xpdr is not maintained in accordance with 413, the requirement does not apply.

@randomhead If the transponder is not maintained in accordance with 91.413 then the aircraft is not legal to fly.

You need deactivate the transponder, say pull out its circuit breaker, to treat the airplane as an no-transponder airplane.


text:
How can I use a magnetic declination chart to calculate true track, magnetic track and magnetic variation?
If I am given values such as 30 degrees south and 75 degrees east with a true track value such as 70 degrees, how would I calculate the magnetic track?
I understand that True track = Magnetic + Variation. But I'm not sure how to use the magnetic declination chart.
This is my attempt at such values:

What exactly don't you understand about the chart?

I edited the post to show what I currently understand on how to tackle the issue, the x marks the 30S 75E with dots going roughly 70 degrees on either side.

The chart shows you lines of equal declination $D$. You identify your location on the chart (which you have done and marked with an X in your second image). Then you determine on which line you are. It looks like the point is between the -26° line and the -28° line, so let's call it $D=-27^\circ$. That gives you a magnetic track of:
$$ \varphi_\text{mag} = \varphi_\text{true} - D = 70^\circ - (-27^\circ) = 97^\circ $$

Thank you, that makes perfect sense.

Oh i see, I thought it was the other way around for some reason. My professor gave me that equation so I'll have to question him about it. Thanks for clarifying.

@SillySquishy Actually, you were right, I mixed up North position with the track direction. My bad :(

Oh haha no worries. Thanks again for the help :)

We've had a question like this before.  I don't recall the title exactly.  The calculation is only for the exact spot where you are located right now (or at some hypothetical point in the flight.)  It has nothing to do with drawing long lines all the way across the map.  If your track crosses multiple lines of declination then you'll be repeating the calculation at multiple different points during the course of the flight or during the course of the flight planning.  But you were asking for one specific point so there is no need to draw a line or think about more than one point.  (A line is a collection of an infinite number of points.)
Why are you drawing a track all the way across the map from 70 N to 70 S?  And why did you draw it along a track line of around 150 true (or 330 true if you are going the other way?)
That would be an interesting flight to make but it is not related to the question you seem to be asking.

I made the track all the way across the map because I didn't know how else to incorporate the true track of 70 degrees into my calculation

Yes i drew it incorrectly, my bad. Thanks for the help, I understand it a lot better now.


text:
Why and how do atmospheric properties sometimes vary from the ISA?
I'm curious as to why sometimes atmospheric properties don't match the ISA's. One reason I am considering is due to calibration discrepancies. By atmospheric properties I mean temperature, Density, Pressure etc.

Let's say the temperature forecast for your town is 18C. Do you expect that every house in the town will experience exactly 18C, across the entire town? If not, why not?

No because temperature varies due to forces like wind.

I respectfully disagree with the closing of this question. ISA model is one of the most profound standards used in aviation. I am aware it is not created solely to serve aviation needs, but understanding the ISA model and how deviations from it affect weather, gauges etc is imperative in aviation.

@Jpe61 Yes, but the question is asking about why there are deviations from the model, which is not related to aviation at all.

@Bianfable I'm only wondering about why these deviations occur with regard to atmospheric conditions, isn't that sort of related to aviation?

An ISA standard atmospheric day is really more like a global average.  Locally and regionally, there will always be deviations from the "norm" based on the natural cycles of the sun.  Overnight the temperature will cool, then the sun will rise and things will warm up again.  This phenomenon also produces variations in the pressure and density over larger areas.
Otherwise, what specifically do you not understand about how and why local and regional conditions are not always "standard"?

I just wanted a general answer as to how & why atmospheric properties aren't always at ISA standard, this answer you have provided is excellent, but is there anything specific that can be pointed to as the culprit?

@SillySquishy The sun.

Thank you, after reading this a few dozen times along with the answer by Jpe61, I fully understand your answer Michael.

The primary reason for the non-ISA conditions is, as Michael Hall stated in his answer, the sun.
Local differences were also explained by Michael, I'd like to add the main contributor to global deviations from ISA: the shape of the earth. As we move further away from the equator, the radiation of the sun hits a surface that is more and more slanted in relation to the direction of the rays, and therefore the energy is divided over a larger area.
Because of this, it is impossible to have equal temperature globally: near the poles its always colder than on the equator. And this opens a whole new can of worms: weather is born. Great differences in temperature over latitudes induces up- and downdrafts, transferring energy(heat), moisture etc. over great distances and creating areas of low and high pressure. Add earths rotation, and it gets really complicated really quick.
This Wikipedia article will give you a brief(ish) description of this phenomenon.
For brevity,I'm not going to go into the effects of the tilted axis of rotation...
In a sense, if atmospheric conditions were always ISA, the weather would always be the same. I'm not wise enough to say what that weather would be...
The reason we need ISA is that have inherent global differences in atmospheric conditions, and that we have changing weather (well, they are very much connected, but best name them both). If we would not have defined ISA conditions, we'd have no reference point, and no way to globally calibrate certain instruments.

This really helped me understand Michael's answer above, thank you for going into great depths about this. I appreciate it a lot.


text:
Are there specific engine TBO requirements for aircraft used in flight instruction?
If I own a plane, say a Piper arrow, and I want to charge 175/hr for the aircraft and 50/hr for instruction, is there any regulation on when to perform engine overhauls (TBO)?
askacfi.com and avweb.com indicate no TBO requirements.
However, 14 CFR Subchapter G - Air Carriers and Operators for Compensation or Hire: Certification and Operations may indicate I do.
What specific regulations show what is or is not required?

Related

Your title and question body are a little different, so I'm not sure what you're asking. Are you asking if flight instruction and rental require an operating certificate per Part  119; or are you asking if aircraft used for flight instruction require a 100hr inspection?

You are correct.  I am aware of the ref'd 91.409.  I'm looking on the proof / reg of TBO reqs. Thanks

Thanks, I reworded your question a little. If I got it wrong then of course just roll back or edit again. You might also like to quote the specific 119 regulation that suggests a specific TBO requirement. But as a general comment, regulations typically say "X is required", not "X is not required". ACs, legal interpretations and other FAA docs might say something like that, though.

Maybe just add part 91 to the title?
I wish I could add any tbo requirement.  I can't find any.  just rumors of them.
The following is my likely incorrect "ref" on "for hire" and "Commercial Operators"
A CFI is a "commercial" Pilot
Subchapter G Air Carriers and Operators for Compensation or Hire: Certification and Operations
Contains
Part 119
View Table of Contents for Part 119
Certification: Air Carriers and Commercial Operators

§91.409   Inspections. (b) Except as provided in paragraph (c) of this section, no person may operate an aircraft carrying any person
(other than a crewmember) for hire, and no person may give flight
instruction for hire in an aircraft which that person provides,
unless within the preceding 100 hours of time in service the aircraft
has received an annual or 100-hour inspection…

You can rent out your airplane without complying with 100 hour inspections provided that you don’t provide both the pilot and the airplane. Insurance will be a lot more, probably 3-4 times as much. If you are renting it out you might have more than 100 hours in a year so you need to make sure you  comply with 100 hour ADs.
I do it with my Cherokee from time to time when I know people who want to learn to fly. The students can use any CFI they want and pay them separately from renting. Depending on how many people want to learn, I have an open pilot policy with only some CFIs and me as named insureds or if there are only a few students, everyone is a named insured.
Edit: The only maintenance requirement for Part 91 operators is 91.409 discussed above. TBO is not specifically mentioned in the FARs so you won’t find a rule saying that you don’t have to comply with manufacturer’s TBOs. I have a folder of 116 Legal Interpretations and NTSB opinions. A search of them finds no mentions of TBOs.
As you point out there are lots of articles that mention it. I'd trust them. This AVWebarticle by maintenance guru Mike Busch says,

Both Lycoming and TCM publish engine TBOs in the form of non-mandatory
service bulletins. Some Part 121/135 operators have Operations
Specifications that require them to comply with all manufacturer’s
service bulletins (even non-mandatory ones), while others have Op
Specs that require compliance only with mandatory service bulletins.

Yup, thanks, what about TBO ?

@chup TBO replacement is a requirement that is built into the operating limitations of Part 135 operators. Along with complying with Service Bulletins. Neither apply to Part 91 and I don’t recall a FAR specifically addressing either.

Yes, Thank you.  This is my issue.  I'm looking for the proof

@chup Since it’s not required by 91 or 135 you probably won’t find it in the FARs. https://www.avweb.com/ownership/the-savvy-aviator-4-debunking-tbo/

So where do you find it in a far that does require it?

@chup AFAIK TBO is not mentioned in the FARs at all. Search with this site:https://www.ecfr.gov TBO

so, if the'yre not "regulated" how are they required?
Is it purely that the faa says "do what the manufacturer says, if you are operating under part X"  God, law documents are terrible

@chup If you are a Part 135 operator you must per §135.63   Recordkeeping requirements. have an operating certificate. It spells out tons of stuff not in the FARs specific to the operator and the aircraft they use. Not my area but you could start here if you are interested. https://www.faa.gov/licenses_certificates/airline_certification/135_certification/